Fair Value Measurements (Details) (USD $) In Millions, unless otherwise specified	Mar. 31, 2012	Dec. 31, 2011
Summary of financial instruments recognized at fair value and fair value measurement used
Cash	$ 367	$ 385
Short-term investments	444	699
Net derivative contracts	46	46
Long-term debt converted to floating interest rates by interest rate swaps - net	56	66
Carrying value of long-term debt and current portion of long-term debt	3,664	3,687
Fair value of long-term debt and current portion of long-term debt	4,212	4,273
Quoted prices in active markets for identical assets (Level 1) [Member]
Summary of financial instruments recognized at fair value and fair value measurement used
Cash	367	385
Short-term investments	444	699
Net derivative contracts	0	0
Long-term debt converted to floating interest rates by interest rate swaps - net	0	0
Other Observable inputs Level 2) [Member]
Summary of financial instruments recognized at fair value and fair value measurement used
Cash	0	0
Short-term investments	0	0
Net derivative contracts	46	46
Long-term debt converted to floating interest rates by interest rate swaps - net	56	66
Unobservable inputs (Level 3) [Member]
Summary of financial instruments recognized at fair value and fair value measurement used
Cash	0	0
Short-term investments	0	0
Net derivative contracts	0	0
Long-term debt converted to floating interest rates by interest rate swaps - net	$ 0	$ 0